Ladder type delay line



Dec. 11, 1962 o. DOHLER ETAL 3,

LADDER TYPE DELAY LINE Original Filed May 19, 1953 6 Sheets-Sheet 1 Dec.11, 1962 o. DOHLER ETAL 3,0

LADDER TYPE DELAY LINE Original Filed May 19, 1953 6 Sheets-Sheet 2 Dec.11, 1962 o. DOHLER ETAL 3,068,432

LADDER TYPE DELAY LINE Original Filed May 19, 1953 6 Sheets-Sheet 3 Dec.11, 1962 o. DOHLER ETAL 3,063,432

LADDER TYPE DELAY LINE Original Filed May 19, 1953 6 Sheets-Sheet 4 Dec.11, 1962 o. DOHLER ETAL LADDER TYPE DELAY LINE 6 Sheets-Sheet 5 OriginalFiled May 19, 1953 Dec. 11, 1962 o. DOHLER ETAL 3,068,432

LADDER TYPE DELAY LINE Original Filed May 19, 1953 6Sheets-Sheet 6United States Patent Ofifice 3,968,432 Patented Dec. 11, 1952 Claimspriority, application France June 28, 1952 17 Claims. (Cl. 333-31) Thepresent invention relates to delay lines of the ladder type, moreparticularly for use in traveling wave tubes and magnetrons. Thisapplication is a division of application Serial No. 356,050, filed May19, 1953, nowPatent No. 2,920,227.

The present invention relates to a very particular type of delay linefor use in electron discharge tubes operating by interaction between theenergies contained respectively in the electron beam and in the field ofan ultra high frequency wave propagated along the line, as for examplein traveling wave tubes. This type of delay line is constructed in theform of a ladder comprising two parallel longitudinal lateral membersand a series of par allel rungs extended between the two lateralmembers, and a metallic base plate upon which the lateral members aresupported with the rungs spaced from the base plate. The length of therungs is approximately equal to half the operating wave length, and fromthis point of view the ladder type delay line operates more efiicientlythan the other known types of delay line such as interdigital or bafilelines. The defect of these other types of line lies in the fact that thewidth of the line is only a quarter wave length or even less.Consequently, for equal length the ladder line may be used in a tube theelectron beam of which is very much wider and the beam current of whichis more intense, whereby the tube can supply a greater power.Furthermore, the coupling resistance between the wave and the beam ishigh with consequent favorable influence on the gain of the tube.

Delay lines of ladder type are already known, however, which have thedisadvantage of opposed electrical and magnetic couplings. as will bemore fully explained hereinafter.

The present invention has for its purpose to improve the known delaylines of ladder type, the primary object being to increase the bandwidth and permit propagation of energy within a wide band of frequenciesindependently of irregularities in the construction of the line. Theprincipal feature of the present invention is the provision of means fortightening up the coupling between the individual circuits constitutingthe delay line.

According to the invention, there is provided a laddertype delay linefor use in microwave tubes, operating by interaction between the beam ofelectrons and an ultrahigh frequency wave traveling through the delayline,

wherein means are provided for tightening the coupling between thesuccessive circuits of the line, by suppressing, or at leastconsiderably reducing, the magnetic coupling between said circuits,characterised in that the rungs are divided into two sets, even and odd,the rungs of at least one set having their ends bent at right angles tothe central portions of these rungs, said ends being secured to asurface different from the surface to which are secured the ends of therungs of the other set.

Also, according to the present invention the magnetic coupling may bereduced to a small value with respect to the electrical coupling byconstructing the delay line such that the mean path followed bymicrowave current between extremities of adjacent rungs on the same sideof the delay line is increased with respect to the direct rectilinearpath between said extremities.

The invention will be more readily understood from the ensuingdescription taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a perspective view of a known delay line of ladder type;

FIGURE 2 is a diagrammatic representation of a chain of circuitsconstituting a delay line of the type shown in FIGURE 1;

FIGURES 3 to 5 illustrate three forms of the invention wherein means areprovided for reducing the electrical coupling of a ladder type delayline;

FIGURE 6 is a graphic representation of the dispersion curves of thelines illustrated in FIGURES 3 to 5;

FIGURES 7 to 9 and 11 illustrate four embodiments of the inventioncomprising means for decreasing the magnetic coupling;

FIGURE 10 is a graphic representation of the dispersion curves of linesin accordance with FIGURES 7 to 9,

FIGURE 12 is a cross section through a crossed field traveling wave tubecomprising a delay line in accordance with FIGURE 9; and

FIGURES 13 and 14 are respectively an axial section and a transversecross section through a magnetron comprising a delay line in accordancewith FIGURE 8 curved to circular shape.

Referring to FIGURE 1 the ladder type delay line of known constructioncomprises two longitudinal lateral members 1 and a series of rungs 2spanning the space between the lateral members. The two lateral membersare mounted on a metal base plate 3 and the length of the rungs 2 isapproximately M2, A being the operating wave length of the line.

FIGURE 2 illustrates how the delay line of FIGURE 1 may be assimilatedto a chain of filter-type circuits having lumped constants. The dottedline 14 in FIGURE I comprising a rung 2 and the closed path along thewalls of the lateral members 1 and across the base plate 3 may beconsidered the equivalent of an anti-resonant circuit comprising a coilL and a capacitor C tuned to M 2. The distribution of potentials on eachrung, as also in each half wave circuit, is such that the potential iszero at the extremities and maximum at the center. Consequently, in thecentral zone of the rung an electrical field of maximum value is coupledwith the electrical fields of the neighboring rungs. This couplingbetween the electrical fields is the equivalent of' the capacitor C ofFIGURE 2. Furthermore, a high frequency current circulates through eachrung the distribution of which is such that it is high at the centralzone of the rung and maximum at the extremities. This current generatesa maximum magnetic field at the extremities of the rung which is coupledto the magnetic fields of the neighboring rungs. This magnetic couplingis the equivalent of an inductive coupling shown on FIGURE 2 as coils Land L between the coils L, of the successive circuits. Finally thediagrammatic showing of FIGURE 2 discloses a chain of anti-resonantcircuits coupled electrically by the capacitors C and magnetically bythe induction circuits L L It is known that in this type of chain theelectrical and magnetic couplings are mutually opposed so that theresonant coupling is very weak. It is also known that a chain of weaklycoupled circuits has a very narrow band width and that the circuits mustbe very closely tuned to the resonant frequency. This phenomenon isrepeated in the ladder type delay line of FIGURE 1 where the dispersion,i.e. the variation of the delay factor as a function of the wave len th,is very substantial, and where the slightest irregularity of mechanicalstructure involves discrepancies between the resonant frequencies of theindividual circuits of the chain. The band width is in fact so narrowthat this property of the ladder type delay line some- 3 times preventsit from propagating any electro-magnetic field whatsoever.

In FIGURE 3, where the same reference numerals designate the sameelements as in FIGURE 1, the electrical coupling between the successiverungs is decreased by in serting a filler member 4 between the baseplate 3 and the rungs 2. The filler member 4 extends longitudinally ofthe delay line or parallel to the locus of the rungs 2, the length ofthe member 4 being greater than either the space between adjacent rungsor the width of each rung has the effect of deforming the electricalfield in the vicinity of the central zones of the rungs whereby aportion of the lines of force is deflected and redirected from each rungtoward the filler member instead of toward the neighboring rung. Thusthere is a smaller number of lines of force actively engaged in theelectrical coupling.

In the embodiment according to FIGURE 4, baffles are positioned in thespaces between the rungs 2, the width of the baflles being such as toextend over the central zones of the rungs. It will be readilyunderstood in this embodiment the capacitor C of FIGURE 2 is replaced bytwo capacitors connected in series, the result being well known in thatit provides a reduced resultant capacity.

FIGURE 5 discloses a combination of the filler member 4 of FIGURE 3 andof the baffies 5 of FIGURE 4.

Decoupling by means of bafiles in accordance with FIGURES 4 and 5 hasthe added advantage, in traveling wave tubes wherein it is well knownthat the beam gradually bends toward the anode as it progresses alongthe interaction space, that the baffles rather than the rungs areexposed to the stream of electrons. Thus the electrons are absorbed bymassive elements which have a good heat dissipation. The upper surfacesof the bafiies 5 which are exposed to the stream of electrons propagatedin the interaction space along the delay line are parallel to the locusof the rungs longitudinally of the line as well asv paralleling therungs transversely of the line. The disposition of the flat electronbeam along the delay line may be generally the same as that illustratedin FIGURE 12 With regard to the base plate 3" and the transverselyextending rungs thereon which are described hereinafter. The electronbeam thus passes in interacting relationship with the rungs on the sidethereof opposite the base plate 3.

The electrical decoupling in accordance with FIGURES 3 to 5 isincreasingly eflective in that order, FIGURE 5 being the most effective.FIGURE 6 is a graphic representation of the ratio between the speed oflight c and the phase propagation velocity v as a function of the wavelength A, from which it is possible to evaluate the dispersion. Thecurve 1 corresponds to the delay line of FIGURE 3 and the curves 2 and 3to the delay line of FIGURE 5 wherein the bat-Hes 5 are of diflferentheights. The straight line 4 indicates the locus of the cut-offfrequencies. The portions of the curves shown in full lines correspondto a propagation at the highest phase velocity among those which arefeasible, and the portions shown in broken lines correspond topropagation with a phase velocity as close as possible to the maximumvelocity of the preceding mode. It will be seen that the more eifectiveis the electrical decoupling the weaker is the dispersion andconsequently the wider will be the band.

FIGURES 7 to 9 illustrate the three embodiments of the invention whereinmeans are incorporated for decreasing the magnetic coupling, thecharacteristic feature common to these three embodiments being that therungs are divided into two groups occupying alternate odd and evenpositions, the rungs of at least one group being bent at right anglesand the extremities thereof being implanted in the surface of a memberseparate from that in which the ends of the other group are implanted.

In FIGURE 7, the odd rungs 2 are conventional, whereas the even rungs 2"are bent downwardly and their ends are implanted into the surface ofelements 13 dis- 4 tinct from the surface of the lateral members 1 inwhich the ends of the rungs 2 are implanted.

In FIGURE 8, both groups of rungs are bent at right angles, one grouphaving their ends implanted in the upper level of a stepped lateralmember 1 and the other group in the lower level thereof, whereby the endof the respective groups are implanted in two distinct surfaces. Thewidth of one group between the bent portions thereof is difierent fromthe width of the rungs of the other group, but the overall length ofeach rung is equal to approximately M2.

In the embodiment shown in FIGURE 9, the rungs 2' and 2" are bent overidentically but in opposite directions, the lateral members 1 and thebase plate 3 being duplicated as indicated respectively at 1, 1", and at3! 3 The magnetic decoupling increases in effectiveness from FIGURES 7to 9 in that order, and FIGURE 10 is a graphic representation similar tothat of FIGURE 6 showing the dispersion curves 1, 2 and 3 correspondingrespectively to the delay lines of FIGURES 7, 8 and 9. As in FIGURE 6the straight line 4 indicates the locus of the cut-off frequencies, andthe portions shown respectively in full, and in broken lines having thesame significance as in FIGURE 6. It will be seen that the moreeffective the magnetic decoupling the weaker the dispersion, the slopeof the curves being gradually reduced and be coming more regular.

There are, of course, many other possibilities of magnetic decoupling,for example as shown in FIGURE 11 where baffies 5' are inserted betweenthe end portions of the rungs, this arrangement being similar withrespect to magnetic coupling to what is shown for electrical coupling inFIGURE 4. In any event, not only in FIGURES 7 to 9 but also in FIGURE11, decoupling is obtained by lengthening or complicating the paththrough which the current circulating on the surface of the metal massshortcircuiting the rungs would have to pass between the adjacent endsof two consecutive rungs.

The invention may be applied in practice to many types of electrondischarge tubes operating on the principle of interaction between a beamand a wave. Delay lines according to the invention are more particularlyintended, however, for use in traveling wave tubes wherein theinteraction between the beam and the wave takes place within the rangeof crossed electrical and magnetic fields, these tubes operating asamplifiers in accordance with one mode of propagation wherein the phasevelocity is of the same sign as the group velocity, or as oscillators inaccordance with a mode of propagation wherein the two velocities haveopposite signs. In FIGURE 6, the full line portions of the curvesdecrease when the wave length increases which indicates that the phasevelocity has the same sign as the group velocity for the mode ofpropagation corresponding to those portions of the curves. The brokenline portions increase on the contrary which corresponds to a phasevelocity opposed to the group velocity. In FIGURE 10, on the contrary,the full line portions increase and the broken line portions decrease orare substantially horizontal. Consequently the delay lines of which thedispersion is indicated by the curves of FIGURES 6, i.e. electricallyuncoupled delay lines, may be used in crossed field tubes operating asamplifiers in accordance with a mode of propagation the phase velocityof which is as high as possible, or as oscillators in accordance with amode the phase velocity of which is lower than the smallest possiblevelocity. The delay lines of which the dispersion is given by FIGURE 10,i.e. magnetically uncoupled delay lines, may be used in crossed fieldtubes operating as oscillators in accordance with a mode of propagationat maximum phase velocity, or as amplifiers in accordance with a mode oflower phase velocity.

FIGURE 12 illustrates by way of example a transverse section through atube including a delay line in accordance with the present invention.The delay line.

is of the type illustrated in FIGURE 9, but it. must be understood thatany other one of the lines described herein could be substituted withoutdeparting from the scope of the invention. In addition to the rungs 2'and 2" and the plates 3 and 3" there are shown in FIGURE 12 the usualnegative electrode 6, the electron beam 7 passing between the electrode6 and the delay line, side walls 8 closing the tube, and magnetic poles9.

The rectilinear shape of the tube shown in FIGURE 12 is in no wayintended to limit the invention. On the contrary, the delay line may bebent to cylindrical shape for use in circular traveling wave tubes.Furthermore the property of low dispersion obtained with the delay linesaccording to the present invention renders them particularly suitablefor use in magnetrons without the necessity for using the connectionsknown as straps which are inserted for artificially reducing the highdispersion of known anodes and for preventing the magnetron from jumpingtoo easily from one frequency of oscillation to another. The delay linesaccording to the present invention, having a low dispersion and beingcomparable to a wide band circuit, already prevent these frequency jumpswithout the use of straps.

FIGURES l3 and 14 are respectively an axial section and a cross sectionthrough a magnetron using a delay line for example as in FIGURE 8 curvedto circular shape, but it must be understood that any other line inaccordance with the invention could be substituted. In these twofigures, there are shown the rungs 2' and 2", the lateral members 1 andbase plate 3 being rolled to cylindrical shape. In the axis of themagnetron is positioned a cathode 11 and the magnetic field is producedby a coil 12.

What is claimed is:

1. A micro-wave delay line comprising at least one metal base plate, apair of lateral members fixed to the base plate and extending along theside edges thereof and a series of parallel rungs extending between thetwo lateral members and fixed thereto on both extremities, said rungsbeing of a length approximating one-half the length of the wave to bedelayed by the line, means being provided for reducing magnetic couplingbetween adjacent extremities of successive rungs on each side of saidseries.

2. A delay line as claimed in claim 1 wherein said rungs are dividedinto two groups positioned alternately along the line, the rungs of atleast one group comprising both end portions bent at right angles to thebody of the rung and at an angle to the longitudinal direction of saiddelay line along said series of rungs.

3. A delay line as claimed in claim 2 wherein the rungs of one groupcomprise both end portions bent at right angles to the body of the rungand at an angle to the longitudinal direction of said delay line alongsaid series of rungs, the rungs of the other group being straight.

4. A delay line as in claim 2 wherein the rungs of each group compriseboth end portions bent at right angles to the body of the rung in thesame direction, the distance between the bent end portions of one groupbeing different from the corresponding distance in the other group.

5. A delay line as claimed in claim 2 wherein the rungs of both groupscomprise both end portions bent at right angles to the body of the rung,the rung of one group being bent in the opposite direction to the rungsof the other group.

6. A delay line as claimed in claim comprising two base plates and apair of lateral members mounted on each base plate, one group of rungsbeing connected to each pair of lateral members.

7. A delay line as claimed in claim 2 wherein said lateral members areof stepped cross section, the rungs of each group being connected atdififerent heights of said cross section.

8. A delay line as claimed in claim 1 comprising bafiles positionedbetween end portions of consecutive rungs and mounted on said base plateadjacent to said lateral members.

9. A delay line as claimed in claim 8 wherein said lateral members areof comb shape, said rungs being connected to said lateral members in theslots defined between the teeth of the combs.

10. A delay line as claimed in claim 1 wherein said lateral membersextend in a straight line.

11. A delay line as claimed in claim 1 wherein each lateral member iscurved to circular shape in a plane perpendicular to the longitudinaldirection of said rungs.

12. A microwave delay line comprising at least one metal base plate, apair of lateral members essentially parallel to said base plate andextending along the side edges thereof and a series of essentiallyparallel rungs extending between the two lateral members and fixedthereto on both extremities, said rungs being of a length approximatingone-half the length of the wave to be delayed by the line, said rungscomprising a rectilinear portion extending at least over a part thereof,said line being electrically equivalent to a chain of coupled circuitsincluding both electrical coupling and magnetic coupling, andlengthening means for the path followed by microwave current betweenextremities of said rectilinear portions of adjacent rungs on each sideof said series with respect to the direct rectilinear path between saidextremities, whereby said magnetic coupling is reduced to a small valuewith respect to said electrical coupling.

13. A delay line as claimed in claim 12 wherein said lateral membersextend in a straight line.

14. A delay line as claimed in claim 12, wherein each lateral member iscurved to circular shape in a plane perpendicular to the longitudinaldirection of said rungs.

15. In a traveling wave tube comprising an envelope, a delay line formicrowave inside said envelope comprising a metal base plate, at leastone pair of lateral members extending longitudinally along the edges ofsaid base plate, and a series of parallel rungs extending between saidlateral members and connected thereto on both extremities, the length ofsaid rungs being substantially equal to one half the length of the waveto be delayed by the line, said rungs comprising a rectilinear portionextending at least over a portion thereof, said line being electricallyequivalent to a chain of coupled circuits including both electricalcoupling and magnetic coupling, and lengthening means for the pathfollowed by microwave current between extremities of said rectilinearportions of adjacent rungs on each side of said series with respect tothe direct rectilinear path between said extremities, whereby saidmagnetic coupling is reduced to a small value with respect to saidelectrical coupling.

16. In a magnetron tube comprising an envelope, a delay line formicrowave inside said envelope comprising a metal base plate, at leastone pair of lateral members extending longitudinally along the edges ofsaid base plate, and a series of parallel rungs extending between saidlateral members and connected thereto on both extremities, the length ofsaid rungs being substantially equal to one-half the length of the waveto be delayed by the line, said rungs comprising a rectilinear portionextending at least in a part thereof, said line being electricallyequivalent to a chain of coupled circuits including both electricalcoupling and magnetic coupling, and lengthening means for the pathfollowed by microwave current between extremities of said rectilinearportions of adjacent rungs on each side of said series, with respect tothe direct rectilinear path between said extremities, whereby saidmagnetic coupling is reduced to a small value with respect to saidelectrical coupling.

17. A ladder-type delay line for use in microwave tubes operating byinteraction between the beam of electrons and an ultra-high frequencywave traveling through the delay line comprising support means and achain of successively coupled circuits each formed by a pair ofsuccessive rungs of the delay line ladder, said rungs having both theirends secured to supporting surfaces of said support means, wherein meansare provided for tightening the coupling between the successive circuitsof the line, by reducing the magnetic coupling between said circuits,characterised in that the rungs are divided into two sets, even and odd,the rungs of at least one set having both their ends bent at angles tothe central portions of these rungs, said ends being secured to asurface diiferent from the surface to which are secured the ends of therungs of the other set.

References Cited in the file of this patent UNITED STATES PATENTS2,511,407 Kleen et al. June 13, 1950 2,745,984 Hagelbarger et a1 May 15,1956 2,768,322 Fletcher Oct. 23, 1956 2,827,588 Guenard et al Mar. 18,1958 2,827,589 Hines Mar. 18, 1958

